**3. Evaluation of soil fertility**

physical and chemical properties by the application of lime and gypsum, chemical fertilization, green fertilization, and use of organic compounds. The choice of sugarcane varieties with a greater productive potential is another technology adopted by producers. For this, it is recommended to consult local or regional research agencies, as well as sugar mills and distilleries, to seek information on the adaptation and productivity of sugarcane varieties in

The average yields of sugarcane, including dry leaves and buds, oscillated around 100 tons of natural matter per hectare. However, by planting improved varieties and correcting and maintaining soil fertility by applying lime, gypsum and fertilization, it is possible to reach productivities of more than 150 tons of natural material per hectare. Complementary irrigation, especially that performed after sugarcane cutting, has resulted in high productivities and greater longevity of sugarcane plantations, as verified by authors in studies conducted in Paracatu, northwest of Minas Gerais, where they obtained an average productivity in two

In order for sugarcane to have high stalk yields in the plant cane cycle and small decreases in ratoon yields, it is necessary to implement measures to maintain or increase soil fertility. Based on that, the present chapter aims to discuss the main technologies, related to soil fertil-

Research has shown that there is a difference among sugarcane varieties in terms of efficiency in the absorption and use of nutrients. There are materials presenting a reasonable production even under conditions of low availability of such nutrients in the soil solution, while other varieties, at times more productive, are consequently more demanding. In the analysis of nutritional efficiency of a variety of sugarcane, its capacity to absorb and use nutrients for the production of dry biomass, protein and sucrose is quantified. The variety that, in the same soil and climatic conditions, accumulates more nutrients is considered more efficient in the absorption process, and the variety that produces a greater mass of sucrose or biomass in relation to mass of an absorbed nutrient is the most efficient in the use of such element [1]. It is desirable that the variety be efficient in both processes, but this is not always achieved.

Currently, there are several sugarcane cultivars with good agronomic, industrial and zootechnical characteristics, such as adaptation to different edaphoclimatic environments, erect growth and resistance to falling, which facilitates harvesting, high yield of culms and sucrose, vigor of sprouts, tolerance to major pests and diseases, and a good dry matter digestibility. It is recommended to plant more than one variety of sugarcane so that, in case of an eventual break of disease resistance or a sudden problem with the cultivar, production will not be significantly compromised. When working with several varieties, varietal management should be adopted to use the good characteristics of each variety to the maximum. Having defined the varieties to be planted, it is necessary to make sure of the quality of seedlings. They should preferably be chosen from nurseries with a good sanity, ages varying between 9

different environments and different cultural managements [1].

cuts of over 200 tons of industrializable culms per hectare per year [1].

ity and mineral nutrition of plants, used for sugarcane production.

and 12 months, and first, or at most, second cutting.

**2. Nutritional efficiency**

170 Sugarcane - Technology and Research

Sugarcane, because it produces large amounts of mass, consequently extracts and accumulates a great quantity of nutrients from the soil. In studies conducted in Brazil, Australia, India, and Florida, it was found that for a production of 120 tons of natural matter per hectare, corresponding to about 100 tons of industrializable culms, the accumulation of nutrients in plant shoots must be 150, 40, 180, 90, 50, and 40 kg of N, P, K, Ca, Mg, and sulfur, respectively. In the case of the micronutrients iron, manganese, zinc, copper, and boron, the accumulations in shoot biomass, also for a production of 120 t, are around 8.0, 3.0, 0.6, 0.4, and 0.3, respectively [2–4]. **Figure 1** shows the accumulation rate of macronutrients in the shoot biomass of RB867515 planted in February and harvested in July of the following year ("year and a half sugarcane").

Due to the high removal of nutrients by the sugarcane harvest, the nutrient supply capacity of the soil must be known to complement chemical and organic fertilization if necessary and, if there is presence of elements at toxic levels, to reduce its concentration by applying lime and gypsum. Normally, nutrient availability and presence of elements at toxic levels in the soil are evaluated by chemical soil analysis. The history of the area, especially fertilizations carried out, and whether or not there were symptoms of deficiency or of toxicity in previous cultures are also of great value [1, 2].

Usually, soil samples are collected from the layers 0–20 and 20–40 cm. The results of the analysis of the layer 0–20 cm will be used to calculate fertilization and liming, and the results of the layer 20–40 cm may be used for calculations of gypsum needed. In the traditional soil sampling system, the area is divided into homogeneous units, taking into account, among others, the history of the area, soil types (color, texture and depth), location and topography (lowlands, slope and plateau), vegetation cover, and previous fertilizations. The most commonly used instruments for collecting soil samples are augers and cutting blades, also known as straight blades. The use of augers in replacement for straight blades has the advantage of a greater speed in collecting

**Figure 1.** Rate of nutrient accumulation in the shoot biomass of RB67515 planted in February and harvested in July of the following year ("year and a half sugarcane").

simple samples, in handling and transporting a small soil volume in field before homogenization of simple samples, and in collecting composite samples. On the other hand, a low volume of collected soil causes variability of soil fertility indexes to increase, making it necessary to collect a high number of simple samples to form a representative composite sample. Even so, the laboriousness of soil sampling using augers is less than when using straight blades. At first, the use of instruments that collect a small soil volume, such as augers, would not be recommended for areas of minimal or no-tillage, where fertilization is performed in planting lines, preferring in such cases straight blades [1]. Regardless of the material used for sampling, care should be taken to always remove the same soil volume from each single sample.

pH increase from 4.0 to 5.0 precipitates aluminum totally and raises the phosphorus content

The use of nitrogen fertilizers, mainly ammoniacal, and the removal of basic cations by harvesting may also contribute to soil acidity, which is why it has been common practice in sugarcane crops to correct soil acidity. Acidification caused by an ammoniacal fertilizer,

SO4 ↔ 2NH<sup>4</sup>

Several materials can be used as soil acidity correctors. The most used are calcitic limestones, magnesium and dolomitic limestones, and calcium and magnesium silicates, called steel plant slags. In these slags, the magnesium oxide content oscillates around 8%, while calcitic limestones have MgO contents lower than 5%, magnesium levels between 6 and 12%, and dolomitic levels above 12%. The efficiency of these products in the correction of soil acidity depends, among other factors, on their particle size, a uniform distribution in the field, and soil water availability. In relation to the corrective dose, there are some methods to estimate the quantity of product to be applied. Such methods are based on the particle size and neutralizing power of the corrective, as well as soil chemical characteristics, mainly calcium, magnesium, potassium, aluminum, and hydrogen contents.

In the majority of Brazilian states, the corrective dose to be applied is estimated by neutralization of exchangeable acidity and increase in calcium and magnesium contents [7], or base saturation [8]. For sugarcane, it has been recommended to increase base saturation (V) to 60%. According to [8], the amount of limestone (QC) to be used, when adopting the base saturation

QC (t ha<sup>−</sup>1) = [(60–V) × T]/PRNT (3)

**(cmolc dm−3) (mg dm−3)**

**pH CaCl2 Ca Mg K Al+3 (H + Al) P**

4.0 1.80 0.66 0.37 1.60 12.56 4.8 4.5 4.40 0.68 0.38 1.00 10.00 5.5 5.0 7.6 0.70 0.35 0.00 6.73 24.2 6.0 10.60 0.70 0.36 0.00 3.66 16.0 7.0 15.00 0.66 0.36 0.00 0.20 8.0

<sup>+</sup> + SO4

. Thus, the acid reaction of ammonium sulfate can be described as:

<sup>−</sup> + 2H<sup>2</sup>

, to neutralize 4H<sup>+</sup>

) 2 SO4

<sup>−</sup> + SO4

<sup>2</sup><sup>−</sup> (1)

Mineral Nutrition and Fertilization of Sugarcane http://dx.doi.org/10.5772/intechopen.72300

is oxidized by Nitrosomonas and

O + 4H<sup>+</sup> (2)

is required.

173

, 200 g of CaCO3

, increase in pH, precipitation of aluminum, and availability of

, is exemplified below:

2

SO4 + 4O2 → 2NO3

originating from the dissociation of (NH<sup>4</sup>

neutralizes 2.0 moles of 2H<sup>+</sup>

−

2

criterion, is calculated by the following expression:

from 4.8 to 24.2 mg/dm3

ammonium sulfate, (NH<sup>4</sup>

+

Since 100 g of CaCO3

Source: adapted from [6].

phosphorus from a Purple Latosol.

**Table 1.** Neutralization of soil acidity using CaCO3

Nitrobacter, producing 2NO3

(NH4)

then 2NH<sup>4</sup>

(NH4)

(**Table 1**).

)2 SO4

In large areas, grid soil sampling has been used. This technique consists in the collection of georeferenced soil samples. Due to georeferencing, it is possible to measure the variability of soil nutrient contents and to apply acid and fertilizer correctives at variable levels. In the traditional collection system, to obtain a composite sample, one must collect between 10 and 30 simple samples, numbers that depend on the size of the area and its homogeneity. On average, five simple samples per hectare are collected. After air-drying the composite sample, approximately 500 g of soil is collected to be packed in a properly identified container and sent to a chemical analysis laboratory.

In Brazil, potassium, calcium, magnesium, sodium, and aluminum are analyzed as for exchangeable contents, and even though there is a great variation in the chemical extractors used by different laboratories, the accuracy of such analyses is high. Phosphorus, however, presents a greater reactivity with the soil, and its dynamics is also more complex. Thus, there are questions about the results of analyses performed in laboratories using different methods and extractors. However, analyses carried out by authors on soils from sugarcane regions in the state of Minas Gerais, Brazil, not fertilized with natural phosphate, indicated that there was no significant difference between available phosphorus levels extracted using Mehlich in relation to levels obtained using ion exchange resin. Sulfur and micronutrient contents varied greatly in relation to method and extractor used in soil chemical analysis, and there is still a great influence of collection time, soil moisture, and sample preparation [5]. Thus, the history of the area is of great value, especially regarding micronutrients, because if there is a record of deficiency in previous crops, it becomes necessary to include such deficient elements in fertilization.
